System and method for measuring pressure applied by a piezo-electric pump

ABSTRACT

A system and method for measuring the pressure provided by a disc pump is disclosed. The disc pump comprises an actuator mounted within the disc pump on a flexible skirt that allows the actuator to oscillate for generating air flow through the cavity of the pump and allows the actuator to be displaced with increasing pressure to a load. The actuator moves from a rest position when air begins flowing through the cavity to a biased position when the load is fully pressurized or depressurized depending on the direction of fluid flow through the cavity. The pump further comprises a sensor which measures the displacement of the actuator at any position between the rest position and the biased position as fluid begins flowing through the cavity to pressurize or depressurize the load. The pressure being delivered by the disc pump is determined as a function of the displacement of the actuator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/371,954, filed Aug. 9, 2010, and is hereby incorporated by reference.

BACKGROUND

1. Field of the Invention

The illustrative embodiments of the invention relate generally to a pump for fluid and, more specifically, to a pump in which the pumping cavity is substantially elliptical in shape having end walls and a side wall with an actuator disposed between the end walls. The illustrative embodiments of the invention relate more specifically to a disc pump having a valve mounted in the actuator and/or one additional valve mounted in one of the end walls.

2. Description of Related Art

The generation of high amplitude pressure oscillations in closed cavities has received significant attention in the fields of thermo-acoustics and pump type compressors. Recent developments in non-linear acoustics have allowed the generation of pressure waves with higher amplitudes than previously thought possible.

It is known to use acoustic resonance to achieve fluid pumping from defined inlets and outlets. This can be achieved using a elliptical cavity with an acoustic driver at one end, which drives an acoustic standing wave. In such a elliptical cavity, the acoustic pressure wave has limited amplitude. Varying cross-section cavities, such as cone, horn-cone, bulb have been used to achieve high amplitude pressure oscillations thereby significantly increasing the pumping effect. In such high amplitude waves the non-linear mechanisms with energy dissipation have been suppressed. However, high amplitude acoustic resonance has not been employed within disc-shaped cavities in which radial pressure oscillations are excited until recently. International Patent Application No. PCT/GB2006/001487, published as WO 2006/111775, discloses a pump having a substantially disc-shaped cavity with a high aspect ratio, i.e., the ratio of the radius of the cavity to the height of the cavity.

Such a pump has a substantially elliptical cavity comprising a side wall closed at each end by end walls. The pump also comprises an actuator that drives either one of the end walls to oscillate in a direction substantially perpendicular to the surface of the driven end wall. The spatial profile of the motion of the driven end wall is described as being matched to the spatial profile of the fluid pressure oscillations within the cavity, a state described herein as mode-matching. When the pump is mode-matched, work done by the actuator on the fluid in the cavity adds constructively across the driven end wall surface, thereby enhancing the amplitude of the pressure oscillation in the cavity and delivering high pump efficiency. The efficiency of a mode-matched pump is dependent upon the interface between the driven end wall and the side wall. It is desirable to maintain the efficiency of such pump by structuring the interface so that it does not decrease or dampen the motion of the driven end wall thereby mitigating any reduction in the amplitude of the fluid pressure oscillations within the cavity.

The actuator of the pump described above causes an oscillatory motion of the driven end wall (“displacement oscillations”) in a direction substantially perpendicular to the end wall or substantially parallel to the longitudinal axis of the elliptical cavity, referred to hereinafter as “axial oscillations” of the driven end wall within the cavity. The axial oscillations of the driven end wall generate substantially proportional “pressure oscillations” of fluid within the cavity creating a radial pressure distribution approximating that of a Bessel function of the first kind as described in International Patent Application No. PCT/GB2006/001487 which is incorporated by reference herein, such oscillations referred to hereinafter as “radial oscillations” of the fluid pressure within the cavity. A portion of the driven end wall between the actuator and the side wall provides an interface with the side wall of the pump that decreases dampening of the displacement oscillations to mitigate any reduction of the pressure oscillations within the cavity, that portion being referred to hereinafter as an “skirt” or a “skirt” as described more specifically in U.S. patent application Ser. No. 12/477,594 which is incorporated by reference herein. The illustrative embodiments of the skirt are operatively associated with the peripheral portion of the driven end wall to reduce dampening of the displacement oscillations.

Such pumps also require one or more valves for controlling the flow of fluid through the pump and, more specifically, valves being capable of operating at high frequencies. Conventional valves typically operate at lower frequencies below 500 Hz for a variety of applications. For example, many conventional compressors typically operate at 50 or 60 Hz. Linear resonance compressors known in the art operate between 150 and 350 Hz. However, many portable electronic devices including medical devices require pumps for delivering a positive or negative pressure that are relatively small in size and quiet during operation so as to provide discrete therapy. To achieve these objectives, such pumps must operate at very high frequencies requiring valves capable of operating at about 20 kHz and higher. To operate at these high frequencies, the valve must be responsive to a high frequency oscillating pressure that can be rectified to create a net flow of fluid through the pump.

Such a valve is described more specifically in International Patent Application No. PCT/GB2009/050614 which is incorporated by reference herein. Valves may be disposed in either the first or second aperture, or both apertures, for controlling the flow of fluid through the pump. Each valve comprises a first plate having apertures extending generally perpendicular therethrough and a second plate also having apertures extending generally perpendicular therethrough, wherein the apertures of the second plate are substantially offset from the apertures of the first plate. The valve further comprises a sidewall disposed between the first and second plate, wherein the sidewall is closed around the perimeter of the first and second plates to form a cavity between the first and second plates in fluid communication with the apertures of the first and second plates. The valve further comprises a flap disposed and moveable between the first and second plates, wherein the flap has apertures substantially offset from the apertures of the first plate and substantially aligned with the apertures of the second plate. The flap is motivated between the first and second plates in response to a change in direction of the differential pressure of the fluid across the valve.

BRIEF SUMMARY OF THE INVENTION

In addressing measurement and control issues of tissue treatment systems, which may include a disc pump or micro-pump, the principles of the present invention may be utilized to measure the pressure being generated by the disc pump to more effectively and economically control the operation of the disc pump. The disc pump includes an actuator that vibrates within a cavity to generate a radial pressure wave to provide a reduced pressure for application to a load or tissue site as described above. Displacement of the actuator may be measured using one or more sensors. Pressure being generated by the disc pump for the tissue site may be determined in response to the measured displacement of the actuator. A drive signal for the actuator may be adjusted to control operation and, consequently, displacement of the actuator to reach a desired pressure at the tissue site.

One embodiment of a disc pump includes a disc pump housing, skirt, actuator, sensor, and electronic circuit. The skirt is fixed to the disc pump housing to support the actuator, and may be any material that is sufficiently flexible to allow the actuator to vibrate. The actuator and the skirt face an opposing base plate to form a cavity within the disc pump wherein radial pressure waves are generated. The actuator may have a first surface and a second surface and be directly or indirectly coupled to the skirt. The sensor may be positioned outside the cavity to sense a position of the actuator with respect to the disc pump housing that corresponds to the pressure being provided. An electronic circuit may be in communication with the sensor and be configured to calculate pressure provided by the disc pump as a function of the position of the actuator with respect to the disc pump housing while the actuator is activated.

In another embodiment, a pump body comprises a substantially elliptical shaped side wall closed at one end by a base wall and the other end by a pair of interior plates to form a cavity within said pump body for containing a fluid wherein a first one of the interior plates adjacent the cavity includes a center portion and a peripheral portion. The pump further comprises an actuator formed by the end plates wherein the second one of the interior plates is operatively associated with the central portion of the first interior plate to cause an oscillatory displacement motion thereby generating radial pressure oscillations of the fluid within the cavity in response to a drive signal being applied to said actuator when in use The pump also comprises a skirt flexibly connected between the side wall and the peripheral portion of the first interior plate to facilitate the oscillatory displacement motion. The pump also comprises a first aperture extending through said actuator to enable fluid to flow through the cavity and a second aperture extending through the base wall to enable fluid to flow through the cavity. A valve is disposed in at least one of said first aperture and second apertures and is adapted to permit the fluid to flow through the cavity in substantially one direction to pressurize or depressurize a load as fluid begins flowing through the cavity, thereby causing said actuator to move toward the base wall from a rest position to a biased position with increasing pressure and flexing of the skirt. The pump further comprises a sensor mounted outside the cavity in a fixed position with respect to said pump body for measuring the displacement of said actuator at any position between the rest position and the biased position as fluid begins flowing through the cavity to pressurize or depressurize the load.

One method for controlling a disc pump includes driving an actuator within a housing of a disc pump using a drive signal. The actuator is mounted within the disc pump by the skirt which is flexible. As the actuator vibrates in response to the drive signal, the pressure created in a load increases while airflow decreases from a free-flow state to a stall state. The pressure being built up in the load by the disc pump may be measured by a sensor as a function of the displacement of the actuator from a rest position in the free-flow state to a biased position in the stall state when the pressure forces the actuator away from the rest position as the skirt flexes with the actuator from its fixed position toward the biased position. Because the actuator generates radial pressure waves within the cavity of the disc pump, such a sensor is preferably positioned outside the cavity of the disc pump so that it does not interfere with the operation of the disc pump itself.

Other objects, features, and advantages of the illustrative embodiments are disclosed herein and will become apparent with reference to the drawings and detailed description that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the present invention are described in detail below with reference to the attached drawing figures, which are incorporated by reference herein and wherein:

FIG. 1A is a schematic, cross-sectional view of a first disc pump having an actuator shown in a rest position according to a first illustrative embodiment;

FIG. 1B is a schematic, cross-sectional view of the first disc pump showing the actuator in a biased position according to a first illustrative embodiment;

FIG. 2A is a graph of the axial displacement oscillations for a fundamental bending mode of the actuator of the first disc pump;

FIG. 2B is a graph of the pressure oscillations of fluid within the cavity of the first disc pump in response to the bending mode shown in FIG. 2A;

FIG. 3 is a zoomed-in view of a first sensor for measuring the displacement of the actuator of the first disc pump according to a first illustrative embodiment;

FIG. 4 is a schematic view of an illustrative receiver of the first sensor indicating the position of the actuator when in the rest position and the biased position;

FIG. 5 is a schematic, cross-sectional view of the disc pump with the actuator shown in the biased position including a zoomed-in view of a second sensor for measuring the displacement of the actuator according to a second illustrative embodiment;

FIG. 6 is a third illustrative sensor including a diffraction grating for measuring displacement of an actuator in a disc pump;

FIG. 7 is a fourth illustrative sensor including a magnetic element for measuring displacement of an actuator in a disc pump;

FIG. 8 is a block diagram of an illustrative circuit of a disc pump for measuring and controlling a reduced pressure generated by the disc pump; and

FIG. 9 is a flow chart of an illustrative process for controlling pressure generated by a disc pump.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1A and 1B are illustrations of a cross-section view of an illustrative disc pump 100 in accordance with illustrative embodiments. As shown, the disc pump 100 may include a pump housing 102 having a substantially elliptical shape including a elliptical wall 101 closed at one end by a base wall 103 and mounted at the other end by legs 105 attached to a circuit board 108 or other substrate to support the pump housing 102. The elliptical wall 101, the legs 105, and base wall 103 together form the pump housing 102. The pump 100 further comprises a pair of disc-shaped interior plates 114, 115 supported within the pump 100 by a ring-shaped skirt 130 affixed to the elliptical wall 101 of the pump body. The internal surfaces of the elliptical wall 101, the base wall 103, the interior plate 114, and the ring-shaped skirt 130 form a cavity 116 within the pump 100. The internal surfaces of the cavity 116 comprise a side wall 118 which is a first portion of the inside surface of the elliptical wall 101 that is closed at one end by end wall 120 wherein the end wall 120 is the internal surface of the end plate 103 and the end wall 122 comprises the internal surface of the interior plate 114 and a first side of the skirt 130. The end wall 122 thus comprises a central portion corresponding to the inside surface of the interior plate 114 and a peripheral portion corresponding to the inside surface of the ring-shaped skirt 130.

Although the pump 100 and its components are substantially elliptical in shape, the specific embodiment disclosed herein is a circular, elliptical shape. In the embodiments shown in FIGS. 1A and 1B, the end wall 120 is shown as being a frusto-conical surface, but may also be generally planar and parallel with the end wall 122. The base wall 103 and elliptical wall 101 of the pump body may be formed from any suitable rigid material including, without limitation, metal, ceramic, glass, or plastic including, without limitation, injection-molded plastic.

The interior plates 114, 115 of the pump 100 together form an actuator 140 that is operatively associated with the central portion of the end wall 122 which is one of the internal surfaces of the cavity 116. One of the interior plates 114, 115 must be formed of a piezoelectric material which may include any electrically active material that exhibits strain in response to an applied electrical signal, such as, for example, an electro-strictive or magneto-strictive material. In one preferred embodiment, for example, the interior plate 115 is formed of piezoelectric material that that exhibits strain in response to an applied electrical signal, i.e., the active interior plate. The other one of the interior plates 114, 115 preferably possess a bending stiffness similar to the active interior plate and may be formed of a piezoelectric material or an electrically inactive material, such as a metal or ceramic. In this preferred embodiment, the interior plate 114 possess a bending stiffness similar to the active interior plate 115 and is formed of an electrically inactive material, such as a metal or ceramic, i.e., the inert interior plate. When the active interior plate 115 is excited by an electrical current, the active interior plate 115 expands and contracts in a radial direction relative to the longitudinal axis of the cavity 116 causing the interior plates 114, 115 to bend, thereby inducing an axial deflection of their respective end wall 122 in a direction substantially perpendicular to the end wall 122 (See FIG. 2A).

In other embodiments not shown, the skirt 130 may support either one of the interior plates 114, 115, whether the active or inert internal plate, from the top or the bottom surfaces depending on the specific design and orientation of the pump 100. In another embodiment, the actuator 140 may be replaced by a device in a force-transmitting relation with only one of the interior plates 114, 115 such as, for example, a mechanical, magnetic or electrostatic device, wherein the interior plate may be formed as an electrically inactive or passive layer of material driven into oscillation by such device (not shown) in the same manner as described above.

The pump 100 further comprises at least two apertures extending from the cavity 116 to the outside of the pump 100, wherein at least one of the apertures contains a valve to control the flow of fluid through the aperture. Although the apertures may be located at any position in the cavity 116 where the actuator 140 generates a pressure differential as described below in more detail, one preferred embodiment of the pump 100 comprises aperture 126 located at approximately the centre of and extending through the base wall 103. The aperture 126 contains at least one end valve. In one preferred embodiment, the aperture 126 contains a valve 128 which regulates the flow of fluid in one direction as indicated by the arrow. Thus, for this embodiment, the valve 128 functions as an inlet valve for the pump.

The pump 100 further comprises at least one aperture from the cavity 116 through the actuator 140, wherein at least one of the apertures contains a valve to control the flow of fluid through the aperture. Although these apertures may be located at any position on the actuator 140 from the cavity 116 where the actuator 140 generates a pressure differential as described below in more detail, one embodiment of the pump 100 comprises a single aperture 131 located at approximately the centre of and extending through the interior plates 114, 115. The aperture 131 contains an actuator valve 132 which regulates the flow of fluid in one direction from the cavity 116 as indicated by the arrow so that the actuator valve 132 functions as an outlet valve from the cavity 116. The actuator valve 132 enhances the output of the pump 100 by supplementing the operation of the inlet valve 128 as described in more detail below.

The dimensions of the cavity 116 described herein should preferably satisfy certain inequalities with respect to the relationship between the height (h) and radius (r) of the cavity 116 which is the distance from the longitudinal axis of the cavity 116 to the side wall 118. These equations are as follows:

r/h>1.2; and

h ² /r>4×10⁻¹⁰ meters.

In one embodiment of the invention, the ratio of the cavity radius to the cavity height (r/h) is between about 10 and about 50 when the fluid within the cavity 116 is a gas. In this example, the volume of the cavity 116 may be less than about 10 ml. Additionally, the ratio of h²/r is preferably within a range between about 10⁻⁶ and about 10⁻⁷ meters where the working fluid is a gas as opposed to a liquid.

Additionally, the cavity 116 disclosed herein should preferably satisfy the following inequality relating the cavity radius (r) and operating frequency (f) which is the frequency at which the actuator 140 vibrates to generate the axial displacement of the end wall 122. The inequality equation is as follows:

$\begin{matrix} {\frac{k_{0}\left( c_{s} \right)}{2\pi \; f} \leq r \leq \frac{k_{0}\left( c_{f} \right)}{2\pi \; f}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack \end{matrix}$

wherein the speed of sound in the working fluid within the cavity 116 (c) may range between a slow speed (c_(s)) of about 115 m/s and a fast speed (c_(f)) equal to about 1,970 m/s as expressed in the equation above, and k₀ is a constant (k₀=3.83). The frequency of the oscillatory motion of the actuator 140 is preferably about equal to the lowest resonant frequency of radial pressure oscillations in the cavity 116, but may be within 20% that value. The lowest resonant frequency of radial pressure oscillations in the cavity 116 is preferably greater than about 500 Hz.

Although it is preferable that the cavity 116 disclosed herein should satisfy individually the inequalities identified above, the relative dimensions of the cavity 116 should not be limited to cavities having the same height and radius. For example, the cavity 116 may have a slightly different shape requiring different radii or heights creating different frequency responses so that the cavity 116 resonates in a desired fashion to generate the optimal output from the pump 100.

In operation, the pump 100 may function as a source of positive pressure adjacent the outlet valve 132 to pressurize a load (not shown) or as a source of negative or reduced pressure adjacent the inlet valve 128 to depressurize a load 150 as illustrated by the arrows. The inlet of the pump 100 as shown is in fluid communication with the load 150 such that the pump 100 functions as a source of negative or reduced pressure adjacent the inlet valve 128. The load 150 may be a tissue treatment system that utilizes negative pressure for treatment. The term “reduced pressure” as used herein generally refers to a pressure less than the ambient pressure where the pump 100 is located. Although the term “vacuum” and “negative pressure” may be used to describe the reduced pressure, the actual pressure reduction may be significantly less than the pressure reduction normally associated with a complete vacuum. The pressure is “negative” in the sense that it is a gauge pressure, i.e., the pressure is reduced below ambient atmospheric pressure. Unless otherwise indicated, values of pressure stated herein are gauge pressures. References to increases in reduced pressure typically refer to a decrease in absolute pressure, while decreases in reduced pressure typically refer to an increase in absolute pressure.

FIG. 2A shows one possible displacement profile illustrating the axial oscillation of the driven end wall 122 of the cavity 116. The solid curved line and arrows represent the displacement of the driven end wall 122 at one point in time, and the dashed curved line represents the displacement of the driven end wall 122 one half-cycle later. The displacement as shown in this figure and the other figures is exaggerated. Because the actuator 140 is not rigidly mounted at its perimeter, but rather suspended by the ring-shaped skirt 130, the actuator 140 is free to oscillate about its centre of mass in its fundamental mode. In this fundamental mode, the amplitude of the displacement oscillations of the actuator 140 is substantially zero at an annular displacement node 42 located between the centre of the driven end wall 122 and the side wall 118. The amplitudes of the displacement oscillations at other points on the end wall 122 are greater than zero as represented by the vertical arrows. A central displacement anti-node 43 exists near the centre of the actuator 140 and a peripheral displacement anti-node 43′ exists near the perimeter of the actuator 140. The central displacement anti-node 43 is represented by the dashed curve after one half-cycle.

FIG. 2B shows one possible pressure oscillation profile illustrating the pressure oscillation within the cavity 116 resulting from the axial displacement oscillations shown in FIG. 2A. The solid curved line and arrows represent the pressure at one point in time In this mode and higher-order modes, the amplitude of the pressure oscillations has a positive central pressure anti-node 45 near the centre of the cavity 116 and a peripheral pressure anti-node 45′ near the side wall 118 of the cavity 116. The amplitude of the pressure oscillations is substantially zero at the annular pressure node 44 between the central pressure anti-node 45 and the peripheral pressure anti-node 45′. At the same time, the amplitude of the pressure oscillations as represented by the dashed line has a negative central pressure anti-node 47 near the centre of the cavity 116 with a peripheral pressure anti-node 47′ and the same annular pressure node 44. For a elliptical cavity, the radial dependence of the amplitude of the pressure oscillations in the cavity 116 may be approximated by a Bessel function of the first kind. The pressure oscillations described above result from the radial movement of the fluid in the cavity 116 and so will be referred to as the “radial pressure oscillations” of the fluid within the cavity 116 as distinguished from the axial displacement oscillations of the actuator 140.

With further reference to FIGS. 2A and 2B, it can be seen that the radial dependence of the amplitude of the axial displacement oscillations of the actuator 140 (the “mode-shape” of the actuator 140) approximates a Bessel function of the first kind so as to match more closely the radial dependence of the amplitude of the desired pressure oscillations in the cavity 116 (the “mode-shape” of the pressure oscillation). Other symmetric and asymmetric functions may also be used to generate pressure oscillations within the cavity 116. In any event, by not rigidly mounting the actuator 140 at its perimeter and allowing it to vibrate more freely about its centre of mass, the mode-shape of the displacement oscillations substantially matches the mode-shape of the pressure oscillations in the cavity 116 thus achieving mode-shape matching or, more simply, mode-matching. Although the mode-matching may not always be perfect in this respect, the axial displacement oscillations of the actuator 140 and the corresponding pressure oscillations in the cavity 116 have substantially the same relative phase across the full surface of the actuator 140 wherein the radial position of the annular pressure node 44 of the pressure oscillations in the cavity 116 and the radial position of the annular displacement node 42 of the axial displacement oscillations of actuator 140 are substantially coincident.

As the actuator 140 vibrates about its centre of mass, the radial position of the annular displacement node 42 will necessarily lie inside the radius of the actuator 140 when the actuator 140 vibrates in its fundamental bending mode as illustrated in FIG. 2A. Thus, to ensure that the annular displacement node 42 is coincident with the annular pressure node 44, the radius of the actuator (r_(act)) should preferably be greater than the radius of the annular pressure node 44 to optimize mode-matching. Assuming again that the pressure oscillation in the cavity 116 approximates a Bessel function of the first kind, the radius of the annular pressure node 44 would be approximately 0.63 of the radius from the centre of the end wall 122 to the side wall 118, i.e., the radius of the cavity 116 (“r”). Therefore, the radius of the actuator 140 (r_(act)) should preferably satisfy the following inequality: r_(act)≧0.63r.

The ring-shaped skirt 130 may be a flexible membrane which enables the edge of the actuator 140 to move more freely as described above by bending and stretching in response to the vibration of the actuator 140 as shown by the displacement at the peripheral displacement anti-node 43′. The flexible membrane overcomes the potential dampening effects of the side wall 118 on the actuator 140 by providing a low mechanical impedance support between the actuator 140 and the elliptical wall 101 of the pump 100 thereby reducing the dampening of the axial oscillations at the peripheral displacement anti-node 43′ of the actuator 140. Essentially, the flexible membrane minimizes the energy being transferred from the actuator 140 to the side wall 118 with the outer peripheral edge of the flexible membrane remaining substantially stationary. Consequently, the annular displacement node 42 will remain substantially aligned with the annular pressure node 44 so as to maintain the mode-matching condition of the pump 100. Thus, the axial displacement oscillations of the driven end wall 122 continue to efficiently generate oscillations of the pressure within the cavity 116 from the central pressure anti-nodes 45, 47 to the peripheral pressure anti-nodes 45′, 47′ at the side wall 118 as shown in FIG. 2B.

As the actuator 140 vibrates in response to the drive signal, the pressure created in the load 150 increases while airflow decreases from a free-flow state to a stall state. The pressure being built up in the load 150 by the disc pump 100 may be measured by a sensor as a function of the displacement (δy) of the actuator 140 from a rest position 136 in the free-flow state as shown in FIG. 1A to a biased position 138 in the stall state as shown in FIG. 1B when the pressure forces the actuator 140 away from the rest position as the skirt 130 flexes with the actuator 140 from its fixed position at the side wall 101 toward the biased position 138. Because the actuator 140 generates radial pressure waves within the cavity 116 of the disc pump 100, such a sensor is preferably positioned outside the cavity 116 of the disc pump 100 so that it does not interfere with the operation of the disc pump 100.

FIG. 3 is a zoomed-in view of a sensor 331 mounted on the circuit board 108 to face the actuator 140 and measure the displacement of the actuator 140 of the disc pump 100. The sensor 331 includes an optical transmitter 332 and optical receiver 334 for use in measuring displacement 130 of the actuator 140. The optical transmitter 332 communicates an optical signal 335 that may be a light wave in a visible or non-visible spectrum. The optical signal 335 is reflected off the surface of the interior plate 115 of the actuator 140 so that the reflected signal is received by the optical receiver 334 regardless of the displacement (δy) of the actuator 140 as shown in FIG. 4. When the actuator 140 is in the rest position 136, a first reflected signal 340 impinges on the optical receiver 334 at the position shown in both FIGS. 3 and 4. As the actuator 140 is displaced from the rest position 136 to the biased position 138, the first reflected signal 340 is correspondingly displaced by a corresponding reflected displacement (δx) as a second reflected signal 342 depending on the displacement (δy) of the actuator 140. Essentially, the image of the reflected signals that impinge on the optical receiver 334 follow a path from the rest position 136 to the fully biased position 138 as shown in FIG. 4. The reflected displacement (δx) is proportional to the displacement (δy) of the actuator 140 which is a function of the pressure provided by the disc pump 100 as described above.

In one embodiment, the optical transmitter 332 may be a laser, a light emitting diode (LED), a vertical cavity surface emitting laser (VCSEL), or light emitting element. The optical transmitter 332 may be positioned on the circuit board 108 and oriented to reflect the optical signal 335 off any point of the interior plate 115 of the actuator 140 as long as that the first reflected signal 340 and the second reflected signal 342 are still received and measured by the optical sensor 334. However, as the actuator 140 oscillates in a fundamental mode to generate airflow as described and shown in FIG. 2A, the amplitude of the displacement oscillations of the actuator 140 may be substantially zero at any annular displacement nodes 42 that are generated. Correspondingly, the amplitudes of the displacement oscillations at other points along the actuator 140 are greater than zero as also described. Therefore, the optical transmitter 332 should be positioned and oriented so that the optical signal 335 is reflected from a position close to the annular displacement nodes 42 to minimize the effect of the high frequency oscillations of the actuator 140 and more accurately measure the displacement (δy) of the actuator 140 as it moves more slowly from the rest position 136 to the biased position 138.

In one embodiment, the optical sensor 334 may include multiple pixels forming a sensor array. The optical sensor 334 may be configured to sense the position of one or more reflected beams at one or more wavelengths. As a result, the optical receiver 334 may be configured to sense the reflected displacement (δx) 144 between the first reflected signal 340 and the second reflected signal 342. The optical receiver 334 may be configured to convert the reflected signals 340 and 342 sensed by the optical receiver 334 into electrical signals by the respective pixels of the optical receiver 334. The reflected displacement (δx) may be measured or calculated in real-time or utilizing a specified sampling, frequency to determine the position of the actuator 140 relative to the pump housing 102. In one embodiment, the position of the actuator 140 is computed as an average or mean position over a given time period. Pixels of the optical receiver 334 may be sized to provide additional sensitivity to detect relatively small displacements (δy) of the actuator 140 to better monitor the pressure being provided by the disc pump 100 so that it can be controlled in real-time.

Alternative methods of computing the displacement of the actuator 140 may be utilized in accordance with the principles of the present invention. It should be understood that determining the displacement of the actuator 140 may be accomplished relative to any other fixed-position element in the pump housing 102. Although generally substantially proportional, the reflected displacement (δx) may equal the displacement (δy) of the actuator 140 multiplied by a scale factor where the scale factor may be predetermined value based in the configuration of the pump housing 102 of the disc pump 100 or other alignment factors. As a result, the reduced pressure within the cavity 116 of the disc pump 100 may be determined by sensing the displacement (δy) of the actuator 140 without the need for pressure sensors that directly measure the pressure provided to a load, but are too bulky and expensive for measuring the pressure provided by the disc pump 100 in a reduced pressure system for example. The illustrative embodiments optimize the utilization of space within the pump housing 102 without interfering with the pressure oscillations being created within the cavity 116 of the disc pump 100.

FIG. 5 is another schematic, cross-sectional view of the disc pump 100 showing the actuator 140 in the biased position 138 including a assumed-in view of another sensor for measuring the displacement of the actuator 140 according to another illustrative embodiment. The sensor is an ultrasonic transceiver 546 that transmits ultrasonic waves 548 to determine the position of the actuator 140 based on the ultrasonic waves 548 reflected by the actuator 140 and received by the ultrasonic transceiver 546. For purposes of simplicity, the ultrasonic waves that echo back to the ultrasonic transceiver 546 are not shown. The ultrasonic transceiver 546 may send raw measurements or processed data regarding the displacement (δy) of the actuator 140 to one or more electronic devices including, for example, a processor to determine the reduced pressure generated by the this pump 100 and other operational characteristics.

With regard to FIG. 6, a diffraction grating 602 for measuring displacement (δy) of the actuator 140 in the disc pump 100 is shown. The diffraction grating 602 may be attached to or integrated with the actuator 140. For example, the diffraction grating 602 may be a reflective optical element attached to or the actuator 140 with adhesives or other fastening means during manufacturing of the disc pump. As shown, a transmitter 607 transmits a multi-spectral optical signal 608 onto the diffraction grating 602. The diffraction grating 602 diffracts the multi-spectral optical signal 608 into several beams with different wavelengths λ1, λ2, λ3, and λ4. The wavelengths of beams λ1, λ2, λ3, and λ4 are detected by a sensor array 610. In one embodiment, the sensor array 610 may include multiple pixels 612, 614, 616, and 618. The pixels 612, 614, 616, and 618 of the sensor array 610 may also be referred to as a pixel array. Alternatively, the sensor array 610 may be a single sensor or pixel element, such as the pixel 614. The transmitter 607 and the sensor array 610 may be connected to circuit board 108 or any other fixed-position element of the pump housing 102 to ensure stability during operation.

In operation, the transmitter 607 may be a light generation circuit or element that transmits the multi-spectral optical signal 608 in the form of multi-spectrum optical signal onto the diffraction grating. The diffraction grating 602 may be an optical component with a regular pattern, which diffracts light of the multi-spectral optical signal 608 into several beams λ1, λ2, λ3, and λ4 and reflects the beams in different directions, as shown in FIG. 6. As is known in the art, the diffraction grating 602 may include grooves or rulings within the grating of the diffraction grating configured to diffuse the λ1, λ2, λ3, and λ4 over the sensor, array 610 during normal operation and displacement of the actuator 140.

The sensor array 610 determines the displacement of the actuator 140 based on the one or more wavelengths received by one or more of the pixels 612, 614, 616, and 618. For example, as shown in FIG. 6 the dispersion of wavelengths λ1, λ2, λ3, and λ4 on the pixels 612, 614, 616, and 618 may correspond to a maximum displacement between the actuator 140 and the circuit board 108. As the actuator 140 moves toward the housing body (i.e., into the cavity), the pixels 612-618 may detect one or more of the wavelengths λ1, λ2, λ3, and λ4. In one embodiment, the measurements from the sensor array 610 may indicate the displacement of the actuator 140. For example, if both λ3 and λ4 are detected by pixel 618, the displacement may be 2 mm indicating optimal displacement for producing a desired pressure in the cavity of the reduced pressure delivery system. The wavelengths λ1, λ2, λ3, and λ4 detected by each of the pixels 612, 614, 616, and 618 may indicate the exact displacement or may provide data utilized to calculate the displacement. In an alternative embodiment, a sensor may be a single pixel configured to sense optical wavelengths in the multi-spectral optical signal 608 so that as the actuator 140 moves, the wavelength sensed by the sensor is indicative of the position of the actuator relative to the housing. In yet another embodiment, an optical sensor with a single cell having known dimensions may be positioned at an optimal location of a certain light spectrum (or any light at all) be sensed by the optical sensor, and, if sensed, a determination may be made that the pump is generating a pressure in a certain tolerance range may be made.

With regard to FIG. 7, a magnetic sensor 702 for measuring displacement (δy) of the actuator 140 in the disc pump 100 is shown. The magnetic sensor 702, which may be a Hall Effect or analogous sensor, is mounted to the circuit board 108 or the pump housing 102. A conductor 706 may be mounted to an actuator 140. The conductor 706 may be metallic, magnetic, or otherwise that is capable of providing for magnetic sensing by the magnetic sensor 702. The magnetic sensor 702 measures a magnetic field 710 between the magnetic sensor 702 and the conductor 706. The magnetic sensor 702 may be calibrated or configured to measure the changing electric field resulting in the magnetic field 710 to determine the displacement between the magnetic sensor 702 and the conductor 706.

Referring to FIG. 8, a block diagram of an illustrative disc pump system 800 that includes a disc pump such as the disc pump 100 described above and a sensor for measuring and, controlling a pressure generated by the disc pump 100 such as the optical sensor 331 including the optical transmitter 332 and the optical receiver 334 is shown. It should be understood that other sensors as described above may also be utilized as part of the disc pump system 800. The disc pump system 800 also comprises a battery 802 utilized to power the disc pump system 800. The elements of the disc pump system 800 are interconnected and communicate through wires, paths, traces, leads, and other conductive elements. The disc pump system 800 may also include a processor 804 and a driver 808 where the processor 804 is adapted to communicate with the driver 808 including communicating a control signal 806 to the driver 808. The driver 808 generates a drive signal 810 that energizes an actuator in the disc pump 100 such as the actuator 140 as described above. The actuator 140 may include a piezoelectric component that generates the radial pressure oscillations of the fluid within the cavity of the disc pump 100 when energized causing fluid flow through the cavity to pressurize or depressurize the load as described above. The processor 804 may be configured to provide in illumination signal 812 to the optical transmitter 332 for illuminating the actuator 140 with an optical beam such as optical beam 335 which is reflected by the actuator 140 to the optical receiver 334 as illustrated by the reflected signals 340, 342 which are also described above. When the reflected signals 340, 342 to impinge on the optical receiver 334, the optical receiver 334 provides a displacement signal 814 to the processor 804 corresponding to the displacement (δy) of the actuator 140. The processor 804 is configured to calculate the pressure generated by the pump 100 at the load as a function of the displacement (δy) of the actuator 140 as represented by the displacement signal 814. In one embodiment, the processor 804 may be configured to average a plurality of reflected signals 340, 342 to determine an average displacement of the actuator 130 over time. In yet another embodiment, the processor 804 may utilize the displacement signal 814 as feedback to adjust the control signal 806 and corresponding drive signal 810 for regulating the pressure at the load.

The processor 804, driver 808, and other control circuitry of the disc pump system 800 may be referred to as an electronic circuit. The processor 804 may be circuitry or logic enabled to control functionality of the disc pump 100. The processor 804 may function as or comprise microprocessors, digital signal processors, application-specific integrated circuits (ASIC), central processing units, digital logic or other devices suitable for controlling an electronic device including one or more hardware and software elements, executing software, instructions, programs, and applications, converting and processing signals and information, and performing other related tasks. The processor 804 may be a single chip or integrated with other computing or communications elements. In one embodiment, the processor 804 may include or communication with a memory. The memory may be a hardware element, device, or recording media configured to store data for subsequent retrieval or access at a later time. The memory may be static or dynamic memory in the form of random access memory, cache, or other miniaturized storage medium suitable for storage of data, instructions, and information. In an alternative embodiment, the electronic circuit may be analog circuitry that is configured to perform the same or analogous functionality for measuring the pressure and controlling the displacement of the actuator 140 in the cavity of the disc pump 100 as described above.

The disc pump system 800 may also include an RF transceiver 820 for communicating information and data relating to the performance of the disc pump system 800 including, for example, the current pressure measurements, the actual displacement (δy) of the actuator 140, and the current life of the battery 802 via a wireless signals 822 and 824 transmitted from and received by the RF transceiver 820. The RF transceiver 820 may be a communications interface that utilizes radio, infrared, or other wired or wireless signals to communicate with one or more external devices. The RF transceiver 820 may utilize Bluetooth, WiFi, WiMAX, or other communications standards or proprietary communications systems. Regarding the more specific uses, the RF transceiver 820 may send the signals 822 to a computing device that stores a database of pressure readings for reference by a medical professional. The computing device may be a computer, mobile device, or medical equipment device that may perform processing locally or further communicate the information to a central or remote computer for processing of the information and data. Similarly, the RF transceiver 820 may receive the signals 824 for externally regulating the pressure generated by the disc pump 100 at the load based on the motion of the actuator 140.

The driver 808 is an electrical circuit that energizes and controls the actuator 140. For example, the driver 808 may be a high-power transistor, amplifier, bridge, and/or filters for generating a specific waveform as part of the drive signal 810. Such a waveform may be configured by the processor 804 and the driver 806 to provide a drive signal 810 that causes the actuator 140 to vibrate in an oscillatory motion at the frequency (f) as described in more detail above. The oscillatory displacement motion of the actuator 140 generates the radial pressure oscillations of the fluid within the cavity of the pump 100 in response to the drive signal 810 to generate pressure at the load.

In another embodiment, the disc pump system 800 may include a user interface for displaying information to a user. The user interface may include a display, audio interface, or tactile interface for providing information, data, or signals to a user. For example, a miniature LED screen may display the pressure being applied by the disc pump 100. The user interface may also include buttons, dials, knobs, or other electrical or mechanical interfaces for adjusting the performance of the disc pump, and particularly, the reduced pressure generated. For example, the pressure may be increased or decreased by adjusting a knob or other control element that is part of the user interface.

A method for measuring pressure generated by a pump to a load is also disclosed. The pump includes an actuator mounted within the pump on a flexible skirt that that forms a cavity within the pump. The flexible skirt allows the actuator to oscillate in order to generate air flow through the cavity of the pump and allows the actuator to be displaced with increasing pressure to the load. The method comprising electrically driving the actuator to cause an oscillatory displacement motion of the actuator within the pump to generate radial pressure oscillations of fluid within the cavity. The method further comprises measuring the displacement of the actuator as fluid begins flowing through the cavity causing the actuator to move from a rest position to a biased position with increasing pressure at the load as accommodated by the flexibility of the skirt. The method also comprises calculating the pressure at the load based on the displacement of the actuator.

Referring more specifically to FIG. 9, a flow chart of an illustrative process 900 for measuring and controlling pressure generated by a disc pump is shown. The process 900 starts at step 902, where an actuator within a housing of a disc pump may be driven by a drive signal. The actuator may be driven by a piezo-electric actuator or device. The actuator may be driven to generate a reduced pressure for application at a tissue site For example, the disc pump may directly or indirectly communicate with a tissue site covered by a drape, as is understood in the art. At step 904, displacement of the actuator may be sensed as the actuator moves from a rest position to a biased position as a result of the pressure increasing within the load. In one embodiment, the rest position occurs when the disc pump when is deactivated or unpowered, and the biased position is reached when pressure within the load is at a maximum value. The displacement of the actuator and the corresponding pressure the load varies between these two positions. The drive signal may be configured, shaped, or otherwise generated by a processor, driver, or control logic of the disc pump for controlling the operation of the actuator and the corresponding pressure being applied to the load.

At step 906, the pressure being generated by the disc pump may be determined as a function of the sensed displacement of the actuator. In one embodiment, the displacement may be determined by reflection or refraction of an optical signal between a housing of the disc pump and the actuator. Similarly, ultrasonic, radio frequency, magnetic, or other optical sensors or transmitter and receiver combinations may be utilized to determine displacement of the actuator. The displacement of the actuator may indicate the pressure being generated by the disc pump for the load. Digital and/or analog electronics may be utilized to determine the pressure applied at the tissue site based on the known differential, factors, losses, and other characteristics of the load such as a tissue treatment system that includes the disc pump as a component. The electronics may utilize any number of static or dynamic algorithms, functions, or sensory measurements to determine the pressure. At step 908, the drive signal is adjusted to control displacement of the actuator in response to determining the pressure being delivered by the disc pump. The drive signal may be generated in response to measurements of feedback signals received from the one or more sensors measuring the displacement of the actuator. In one embodiment, the amplitude of the drive signal may be increased to increase the reduced pressure generated by the disc pump and correspondingly communicated to the tissue site Similarly, the amplitude or the shape of the drive signal may be modified to drive the actuator of the disc pump for decreasing or maintaining pressure at the load.

The illustrative embodiments provide a low cost system for indirectly monitoring the pressure generated by a disc pump by interpreting data provided by a sensor in the disc pump that measures the displacement of an actuator relative to fixed-position components within the disc pump when the actuator moves from a rest position to a biased position. It should be understood that the sensor or any component thereof such as the optical transmitter of an optical sensor may be connected directly to the actuator for measuring the displacement by reflecting the optical signal off of the pump housing or any other fixed position on the disc pump. The illustrative embodiments reduce the equipment, space, and cost to monitor pressure being generated by the disc pump beyond that available utilizing traditional pressure sensors and monitors that directly sense the pressure generated by a pump at the load.

The previous detailed description is one of a small number of embodiments for implementing the invention and is not intended to be limiting in scope. One of skill in this art will immediately envisage the methods and variations used to implement this invention in other areas than those described in detail. The following claims set for a number of the embodiments of the invention disclosed with greater particularity. 

1. A pump comprising: a pump body having a substantially elliptical shaped side wall closed at one end by a base wall and the other end by a pair of interior plates to form a cavity within said pump body for containing a fluid, wherein a first one of the interior plates adjacent the cavity includes a center portion and a peripheral portion; an actuator formed by the end plates wherein the second one of the interior plates is operatively associated with the central portion of the first interior plate to cause an oscillatory displacement motion thereby generating radial pressure oscillations of the fluid within the cavity in response to a drive signal being applied to said actuator when in use; a skirt flexibly connected between the side wall and the peripheral portion of the first interior plate to facilitate the oscillatory displacement motion; a first aperture extending through said actuator to enable fluid to flow through the cavity; a second aperture extending through the base wall to enable fluid to flow through the cavity; a valve disposed in at least one of said first aperture and second apertures and is adapted to permit the fluid to flow through the cavity in substantially one direction to pressurize or depressurize a load as fluid begins flowing through the cavity, thereby causing said actuator to move toward the base wall from a rest position to a biased position with increasing pressure and flexing of the skirt; and, a sensor mounted outside the cavity in a fixed position with respect to said pump body for measuring the displacement of said actuator at any position between the rest position and the biased position as fluid begins flowing through the cavity to pressurize or depressurize the load.
 2. The pump of claim 1 wherein the ratio of the radius of the cavity (r) extending from the longitudinal axis of the cavity to the side wall to the height of the side wall of the cavity (h) is greater than or equal to 1.2. 3.-9. (canceled)
 10. The pump of claim 1 wherein said skirt is a flexible membrane.
 11. The pump of claim 10 wherein the flexible membrane is formed from plastic.
 12. The pump of claim 11 wherein the annular width of flexible membrane is between about 0.5 and 1.0 mm and the thickness of the flexible membrane is less than about 200 microns.
 13. The pump of claim 10 wherein the flexible membrane is formed from metal.
 14. The pump of claim 13 wherein the annular width of flexible membrane is between about 0.5 and 1.0 mm and the thickness of the flexible membrane is less than about 20 microns. 15.-20. (canceled)
 21. The pump of claim 1 further comprising an electronic circuit in communication with said sensor and configured to calculate the pressure at the load as a function of the displacement of said actuator.
 22. The pump of claim 21 wherein the electronic circuit is further, configured to calculate the rate of change of the pressure at the load.
 23. The pump of claim 1 wherein said sensor is an optical sensor configured to illuminate and measure the displacement of said actuator.
 24. The pump of claim 23 wherein the optical sensor illuminates an annular displacement node of the oscillatory displacement motion of said actuator.
 25. The pump of claim 23 wherein said optical sensor comprises an optical transmitter and an optical receiver.
 26. The pump of claim 25 wherein the optical transmitter includes a light emitting diode that illuminates said actuator with an optical beam, and wherein the optical receiver includes a light sensor array of pixel elements that sense reflections of the optical beam as of the reflections move along the array of pixel elements corresponding to the displacement of said actuator as said actuator moves from the rest position to the biased position.
 27. The pump of claim 25 further comprising an electronic circuit in communication with the optical receiver and configured to calculate the pressure at the load as a function of the displacement of said actuator.
 28. The pump of claim 23 wherein the optical sensor comprises an illumination source for providing an optical beam having a multi-frequency spectrum, a diffraction grating disposed on said actuator for reflecting the optical beam as a plurality of reflected beams at different wavelengths within the multi-frequency spectrum, and an optical receiver for receiving the reflected beams, each of which corresponds to a different displacement of said actuator as said actuator moves from the rest position to the biased position.
 29. The pump of claim 1 wherein said sensor is a magnetic sensor.
 30. The pump of claim 1 wherein said sensor is and RF sensor.
 31. A method for measuring pressure generated for a load by a pump having an actuator mounted within the pump on a flexible skirt that allows the actuator to oscillate for generating air flow through a cavity of the pump and allows the actuator to be displaced with increasing pressure to the load, said method comprising: driving the actuator to cause an oscillatory displacement motion of the actuator to generate radial pressure oscillations of fluid within the cavity; measuring the displacement of the actuator as fluid begins flowing through the cavity causing the actuator to move from a rest position to a biased position with increasing pressure at the load and flexing of the skirt; and calculating the pressure at the load based on the displacement of the actuator. 32.-43. (canceled)
 44. A disc pump comprising: a pump body having an end wall closing one end of the pump body, the end wall having an aperture for airflow through the aperture; an actuator having a peripheral portion and a flexible skirt portion extending from the peripheral portion to the pump body wherein the actuator closes the other end of the pump body to form a cavity therein, the actuator including an aperture for airflow through the aperture, and configured to vibrate in an oscillatory motion to generate airflow from one aperture to the other aperture for building pressure at a load; a valve disposed in one of the apertures and adapted to permit airflow through the cavity in substantially in one direction to pressurize or depressurize the load thereby causing the actuator to move from a rest position to a biased position with increasing pressure at the load; and a sensor configured to measure the displacement of the actuator as the pressure builds within the load and to calculate the pressure as a function of the displacement.
 45. A disc pump according to claim 44, wherein the sensor is mounted outside the cavity in a fixed position with respect to said pump body.
 46. The pump of claim 44 wherein said sensor is an optical sensor configured to illuminate and measure the displacement of the actuator.
 47. The pump of claim 46 wherein the optical sensor illuminates an annular displacement node of the oscillatory motion of the actuator.
 48. The pump of claim 47 wherein said optical sensor comprises an optical transmitter and an optical receiver.
 49. The pump of claim 48 wherein the optical transmitter includes a light emitting diode that illuminates the actuator with an optical beam, and wherein the optical receiver includes a light sensor array of pixel elements that sense reflections of the optical beam as of the reflections move along the array of pixel elements corresponding to the displacement of the actuator as the actuator moves from the rest position to the biased position.
 50. The pump of claim 48 further comprising an electronic circuit in communication with the optical receiver and configured to calculate the pressure at the load as a function of the position of said actuator.
 51. The pump of claim 46 wherein the optical sensor comprises an illumination source for providing an optical beam having a multi-frequency spectrum, a diffraction grating disposed on said actuator for reflecting the optical beam as a plurality of reflected beams at different wavelengths within the multi-frequency spectrum, and an optical receiver for receiving the reflected beams, each of which corresponds to a different position of said actuator.
 52. The pump of claim 44 wherein said sensor is a magnetic sensor.
 53. The pump of claim 44 wherein said sensor is an RF sensor.
 54. The pump of claim 44 wherein said sensor is an ultrasonic sensor.
 55. The pump of claim 44 wherein the load is calculated as a function of the average position of a sensed part of the actuator. 